Effects Of Sethoxydim On Photosynthetic Characteristics In Leaves Of "Zhangza 10" Foxtail Millet And The Residue Analysis

"Zhangza" Foxtail Millet has the advantages of high quality and high yield,drought-resistant and water-saving,saving labor and time,strong resistance,suitable for mechanized cultivation,etc.At present,it has been promoted and planted in the world.12.5%sethoxydim EC is a special herbicide for Zhangza field.In order to scientifically regulate the use of sethoxydim,ensure human health and sustainable development of the field ecosystem,we studied the effects of sethoxydim on the photosynthetic physiology in leaves of Zhangza at elongation stage(8 leaves stage),and the dissipation and residue of sethoxydim in a zhangza foxtail millet field ecosystem at the recommended period(3-5 leaves stage).Through pot experiment and completely random design,we studied the photosynthetic physiological characteristics of different concentrations(0?0.75?1.5?3?6 L ai hm-2)of 12.5%sethoxydim EC at elongation stage.The photosynthetic pigment content,photosynthetic carbon assimilation key enzyme,gas exchange parameter,P700 parameter,and chlorophyll fluorescence parameter,etc.were measured.We studied the residue and digestion of sethoxydim in zhangza field though foliar application of 12.5%sethoxydim EC with the maximum recommended dose(1.5 L ai hm-2)and 1.5 times the maximum recommended dose(2.25 L ai hm-2)in 3 to 5 leaves stage.The method for the residue detection of millet plants(straw),millet,glutinous rice,and soil using ultra-high performance liquid chromatography-tandem triple quadrupole mass spectrometry combined with QuEChERS pretreatment technology was established,and the residual digestion dynamics and final residues in Dingxiang County,Lingchuan County and Taigu County were determined using this method.The main results are as follows:1.With the increase of the dose of sethoxydim,photosynthetic pigment content(Chla,Chlb,Car,total Chl),these activities of phosphoenolpyruvate carboxylase(PEPC),NADP-malate dehydrogenation(NADP-MDH)and pyruvate phosphate dual kinase(PPDK),net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),Pm,Y(?),ETR(?),Fm,Fv/Fo,Fv/Fm,Y(?),ETR(?),and qP decreases;The activities of NADP-malic enzyme(NADP-ME),and ribulose-1,5-bisphosphate carboxylase(Rubisco),stomatal limit values(Ls)and Y(ND)showed a trend of increasing first and then decreasing.Ci showed a trend of decreasing first and then increasing.Y(NA),F0 and NPQ showed an upward trend.Low concentration(?1.5 L ai hm-2)damage to foxtail millet photosynthetic activity is relatively light,foxtail millet can maintain the degree of photosynthesis by adjusting the activity of NADP-ME and Rubisco,enhance heat dissipation,when the concentration is higher than 1.5 L ai hm-2 will cause irreversible damage to the photosynthetic activity of foxtail millet,which seriously restricts the intensity of photosynthesis.The treatment of sethoxydim prevented the synthesis of photosynthetic pigments,reduced the stomatal conductance,inhibited the photosynthetic activity,destroyed the normal photosynthetic carbon assimilation,and led to the weakening of photosynthesis,which affected the normal growth and development of Zhangza 10.2.Foxtail millet plants(straw),millet,cavings and soil were extracted with 1%acetic acid and acetonitrile,and purified by different purifying agents(plant/straw:100 mg PSA+ 50 mg GCB + 300 mg anhydrous magnesium sulfate;millet/cavings:100 mg C18+50 mg GCB+300 mg anhydrous magnesium sulfate;Soil:150 mg C18+300 mg anhydrous magnesium sulphate),0.02%formic acid water and acetonitrile as mobile phases,and liquid chromatography mass spectrometry/mass spectrometry Quantification by external standard method.The limit of quantification(LOQ)of the method in plants,millet,cavings and soil were 2.20,1.60,1.80,2.50,3.00 pg/kg.At the addition levels of 0.01,0.1,and 1 mg/kg,the average recoveries of sethoxydim in soil,plant,millet,and cavings were 87.67%to 109.93%,86.85%to 114.59%,93.26%to 117.64%,and 84.81%to 98.63%,the standard deviation was between 2.29%and 11.48%.3.Based on the established method,the contents of sethoxydim in millet plant(straw),millet,cavings and soil in Zhangzag 10 of Dingxiang,Lingchuan and Taigu in Shanxi Province were determined.Through the digestion dynamic test,the degradation of sethoxydim in plants and soil accorded with the first-order chemical reaction kinetic equation C=C0e-kt,and the theoretical half-lives in plants and soil were 12.72h?29.28 h and 18.48 h?33.6 h,sethoxydim is an easily degradable pesticide.The results of the final residue test showed that the residual amounts in the straw,millet,cavings,and soil were lower than the limit of quantification at the harvesting time when the spraying dose was 1.5 L ai ha-1 and 2.25 L ai ha-1,and both were less than the MRL of domestic and international standards.Therefore,the sethoxydim used in Zhangzai field once a year does not exceed 2.25 L ai hm 2,and the final residues in foxtail millet straw,millet,cavings and soil all meet the residue limit standard and are safe to humans and animals.